Here's the rub for companies: A good part of the key markets they serve already own smartphones and use them to connect various Internet services. How do you grow from there?

Services from Facebook to Firefox are looking to emerging markets for the next few billion people. They are not only targeting the obvious high-population countries such as India and China, but also see potential in Latin America, Africa and just about everywhere beyond the U.S., Canada, western Europe and a few Asian nations.

One message has been clear this week at the Mobile World Congress wireless show in Barcelona, Spain: Even as the affluent crave the latest iPhones or Android phones, most of the world can't afford the hundreds of dollars they cost.

So there's been a push to get mobile devices cheap enough to reach emerging markets without sacrificing so much performance that first-time smartphone owners will give up on the Internet and forgo a second smartphone down the road.

It's a delicate balance.

When Motorola Mobility introduced the low-cost Moto G smartphone last fall, the company emphasized how it was bringing the features of high-end smartphones to a device that starts at just $179. Even then, it had to sacrifice camera resolution and connectivity to the faster 4G LTE cellular networks. And $179 is still expensive for many.

At the Barcelona show this week, Nokia Corp. unveiled the Nokia X series, starting at $122.

"In the growth market ... a couple of bucks make a huge difference," said Timo Toikkanen, Nokia's executive vice president for mobile phones.

Still too expensive? Try some of the $50 to $70 smartphones based on Firefox OS, a system adapted from the popular Firefox Web browser. Mozilla, the organization behind Firefox, announced a partnership with Chinese chipmaker Spreadtrum Communications Inc. to create a blueprint for any phone maker to make $25 smartphones.

Microsoft Corp., meanwhile, said it was relaxing hardware requirements to keep phone costs down. For instance, phones no longer need physical camera and control buttons. Those can now be done through software instead.

It is also working with Qualcomm Inc. on blueprints for any phone maker to quickly design a Windows phone. While global brands such as Apple and Samsung reign in industrialized countries, smaller, regional manufacturers thrive in emerging markets because of lower distribution costs and better tailoring to local needs.